The specific aim of this project is to study prospectively a cohort of children and their families to determine the extent to which childhood respiratory illness, childhood exposure to cigarette smoke (active and passive), familial factors (environmental/genetic) and airways hyperreactivity are risk predictors for adult chronic airways obstruction as assessed by their capacity to affect patterns of increase in lung function that accompany growth and development. The cohort will be observed annually in their homes. At each visit standardized respiratory illness, smoking and demography questionnaires will be administered. Forced expiratory volumes will be obtained with an 8-liter portable spirometer. Each year airways reactivity will be assessed in 50% of the study population using eucapneic hyperventilation with subfreezing air. Density-dependence of flow at specific lung volumes will also be evaluated in this 50% sample. The analyses of the data will focus on those epidemiologic risk factors which define impaired development of lung function during growth and excess decline of lung function during adult life. Factors which characterized the cohort at its inception will be studied to determine their ability to predict impaired growth and excessive decline of lung function. Methods of analyses will include logistic regression, Markov-type models and analyses of curves of change of lung function with growth. The proposal seeks to define early life risk predictors for CAO and thereby defined those at special risk prior to the occurrence of clinically disabling disease.